Benzothiazole disulfide and benzothiazole sulfenamides are used extensively as accelerators in the vulcanization of rubber. One process for the manufacture of benzothiazole disulfide comprises the oxidation of sodium 2-mercaptobenzothiazole to bis(2-benzathiazolyl) disulfide and one process for the manufacture of benzothiazolyl sulfenamides comprises the oxidation of an amine salt of 2-mercaptobenzothiazole to benzothiazole sulfenamide. After the products are recovered, effluent from both processes contain oxidized forms of 2-mercaptobenzothiazole including significant quantities of benzothiazole sulfonates which oxidized products represent an economic loss based on conversion of starting materials and which pose ecological problems when the effluent is discharged into a river or tributary thereof.
The reaction of hydrogen sulfide with sulfonates has not been extensively studied but the studies which have been reported indicate that the yields are too low for practical interest. Only compounds containing an activated sulfur group, such as, in 2,4-dinitrobenzene-sulfonic acid or potassium anthraquinone-2-sulfonate appear to undergo significant reaction. Surprisingly, now it has been found that hydrogen sulfide reacts essentially quantitatively with azole-sulfonates and azole-sulfinates to give the corresponding 2-mercaptoazole. Application of this novel reaction provides a means by which benzothiazole sulfonates may be removed from effluent and 2-mercaptobenzothiazole or its salts recovered and recycled for conversion to additional disulfide or sulfenamide. Thus, this invention provides a means for purifying effluent streams while recovering valuable by-products.